Multi-layer molding nozzle

ABSTRACT

A multi-layer forming nozzle includes a valve member which can open and close a flow passage for molten resin which forms an intermediate layer of a multi-layer molded product by injection molding. The valve member is operated in response to resin pressure differentials at the front and back of the valve member to accurately switch from a multi-layer operation to a single layer operation and vice versa. A three-layer nozzle in accordance with the invention has a nozzle body provided interiorly with a first resin path, a second resin path and a third resin path in the form of a concentric circle bending to the same injection opening. The valve member is located either in a mouth portion of the third resin path in the central portion positioned internally of a mouth portion of the second resin path or a mouth portion of the second resin path in the intermediate portion positioned internally of the first resin path. The valve member is moved forward and backward in response to resin pressure differentials to open and close the valve member.

The present application is a continuation of application Ser. No.07/381,650, filed Jun. 30, 1989 now U.S. Pat. No. 5,030,077.

FIELD OF THE ART

This invention relates to a multi-layer molding nozzle used when asynthetic resin molded product whose sectional construction ismultilayered is injection molded.

BACKGROUND

A conventional multi-layer molding nozzle comprises a multiple nozzle inwhich a nozzle body having a central mouth portion at a tip thereof isprovided interiorly with a plurality of concentric resin paths, anddifferent molten resins in the respective resin paths can becavity-injected from said mouth of the nozzle

The formation of a synthetic resin molded product into a multi-layercauses the quality of a thin-wall molded product (such as a beveragecontainer) to be further improved by the resin present as anintermediate layer However, this poses a problem in that because of theprovision of the intermediate layer, the shock resistance of the productis lowered or the cost of the product is lowered or the cost of theproduct increases, as compared with single layer products.

In view of the foregoing, an attempt has been made to use a conventionaldouble or three-layer nozzle to control injection pressure, time,injection timing or the like of the molten resin which forms anintermediate layer so as to injection-mold a product partly having anintermediate layer. However, it has been very difficult to mold anintermediate layer within a predetermined range in terms of resinpressure.

Alternatively, a multiple nozzle is used in which a central path of amultiple resin path is made movable so that orifices of resin paths areselectively opened and closed to control molten resin, as disclosed inJapanese Patent Application Laid-Open No. 60-34819. However, in thiscase, a special valve device is required to control a flow of moltenresin entering the central path passing through the orifice forinjection, and in addition, the valve device is mechanically operated,and the nozzle has an extremely complicated construction.

DISCLOSURE OF THE INVENTION

This invention has been achieved in order to solve the above-describedproblems with respect to the conventional multiple nozzle. An object ofthis invention is to provide a new multi-layer molding nozzle which issimple in construction, and in which a flowpassage of molten resin whichis to form an intermediate layer is opened and closed by a valve memberto be operated by resin pressure to always accurately switch a multiplelayer to a single layer and vice versa.

This invention having the aforesaid object overcomes the aforementionedproblem encountered in the prior art by a three-layer nozzle in which anozzle body is interiorly provided with a first resin path, a secondresin path and a third resin path having the same injection opening in aconcentric fashion, in which multiple nozzle, a mouth portion of thecentral third resin path located internally of a mouth portion of thesecond resin path is constituted by a valve member which is movedforward and backward by resin pressure of the third resin path and thesecond resin path to open and close the second resin path, and a mouthportion of the intermediate second resin path located internally of thefirst resin path is constituted by a valve member which is moved forwardand backward by resin pressure of the second resin path and the firstresin path to open and close the second resin path.

In the above-described structure, the molten resins of the respectiveresin paths applied with injection pressure are simultaneously injectedfrom the mouth portion of the respective resin paths to cavities throughthe mouth portion of the nozzle. When the injection pressure of thesecond resin path is removed during the injection, the valve member ismoved forward or backward by the resin pressure of the first or thirdresin path to close the second resin path to stop an outflow of themolten resin from the second resin path. Because of this, the moltenresins of the first and third resin paths are merely injected to thecavity.

When injection pressure is applied to the second resin path, the valvemember is moved backward or forward due to a difference in pressurereceiving area in the valve member to open the second resin path, andthe molten resin is injected to the cavity together with the moltenresin of the other resin paths.

Accordingly, when the same kind of molten resin is used for the firstand third resin paths and the different kind of molten resin is used forthe second resin path, a molded product produced thereat is composed ofa 2-kind 3-layer portion and a single layer portion.

This invention will be further described in detail by way of examplesshown in the drawings

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings show embodiments of a multilayer molding nozzle accordingto this invention in which:

FIG. 1 is a sectional view of a first embodiment;

FIG. 2 is a sectional view of a second embodiment thereof;

FIG. 3 is a sectional view in which a hot runner block is mounted;

FIGS. 4 and 5 are respectively sectional views showing the moldingsteps; and

FIGS. 6 to 8 are respectively sectional view of a preform having abottom and a container.

BEST MODE FOR CARRYING OUT THE INVENTION

A nozzle body 1 is provided with an injection opening 2 formed centrallyin the end surface of nozzle body 1. A first resin path 3, a secondresin path 4 and a third resin path 5 are provided in the interior ofthe body 1 in a concentric fashion.

The three resin paths are defined by the cooperation between the firsthollow core member 6, the second hollow core member 7 having a spacer onthe side thereof and the interior of the body 1. The core members 6 and7 are inserted in order through an opening at the rear end of the nozzlebody 1.

The three-layer nozzle shown in FIG. 1 has a construction in which amouth portion 3a of the first resin path 3 connected to the injectionopening 2 is internally provided with a mouth portion 4a of the resinpath 4, and a mouth portion 4a of the second resin path 4 is internallyprovided with a mouth portion 5a of the third resin path 5, the mouthportion 5a being formed from a valve member 8.

The valve member 8 comprises an annular body which is inserted so as toappear in the inner side of the end of the second core member 7. Theinside diameter of the valve member 8 is substantially equal to theinside diameter of the mouth portion of the first resin path 3 and issmaller than the diameter of the third resin path 5, and the fore end 8aand the rear end 8b thereof are formed into a tapered surface on whichresin pressure is exerted.

The ratio of a pressure receiving area of the ends 8a located in thesecond resin path 4 to the pressure receiving area of the end 8b locatedin the third resin path 5 is preferably greater than 0.5 and less than 4in the projection plane. As long as the aforementioned ratio issatisfied, the valve member 8 will be moved downwardly into the end ofthe second core member 7 to maintain the second resin path 4 open evenif the resin pressure of the third resin path 5 is somewhat greater thanthe resin pressure in the second resin path 4 during the injectionoperation. When the injection pressure of the second resin path 4 ismade remarkably lower than (sufficiently low to overcome the ratio ofthe surface areas) the resin pressure of the third resin path 5, thevalve member 8 will immediately move forward due to the resin pressureof third resin path 5 exerting on the rear end 8b to close the secondresin path 4.

Accordingly, the valve member 8 is operated to open and close the secondresin path 4 according to a difference between the resin pressuresexerted on the opposite ends of the valve 8 to control the injection ofthe molten resin from the second resin path 4.

A second embodiment of a three-layer nozzle in accordance with thepresent invention is shown in FIG. 2. In this embodiment the opening andclosing of the second resin path 4 may be accomplished by the resinpressure of the first resin path 3, and the valve member is inserted inthe end of the first core member 6.

In this case, since the second resin path 4 is closed by the backwardmovement of the valve member 8, the end 7a of the second core member 7is reduced in diameter and extends to the front of the first resin path3, the mouth portion 5a of the third resin path is made to extend to theinner side of the mouth portion 3a, the second resin path 4 is opened atthe side of the end 7a of the second core member 7, and the mouthportion 4a is constituted by the valve member 8 located at the peripheryof the end 7a of the second core member 7 inserted into the end of thefirst core member 6. The inside diameter of the valve member 8 is largerthan the outside diameter of the end portion 7a of the second coremember 7 to form a portion of the second resin path 4 between it and thesecond core member 7, and when the rear end 8b comes into contact with atapered shoulder 9 formed in the outer surface of the second core member7, the second resin path 4 is closed.

The ratio of a pressure receiving area of the fore end 8a to thepressure receiving area of the rear end 8b of the valve member 8 ispreferably greater than 0.5 but less than 4 in the projection plane

The resins supplied to the respective resin paths are suitably selecteddepending on the products to be molded, and in case of 3-kinds of resinsand 5-layers, different resins are supplied to the respective resinpaths. In the case where a product having 2-kinds of resins and 3-layersis injection molded, the resin material of the first resin path 3 is thesame as that of the third resin path 5.

The required number of the aforesaid three-layer nozzles are used whilebeing mounted on a hot runner block 10 (FIG. 3). This embodiment showsthe case where a 2-kind of resin and 3-layer molded product is molded,in which the hot runner block 10 is interiorly provided with hot runners13 and 14 connected to sprue bushes 11 and 12, respectively, arranged onthe side thereof, and the hot runner 13, the hot runner 14 and a branchpath 15 of the hot runner 14 are connected to the second resin path 4,the third resin path 5 and the first resin path 3, respectively, so thatthe same type of resin is injected from the first and third resin paths3 and 5, and a different type of resin is injected from the second resinpath 4.

The manner in which a three-layer product having an intermediate layeris molded using the three-layer nozzle shown in FIG. 1 will now bedescribed.

First, when injection pressure is applied to the first and third resinpaths 3 and 5 to inject resin A therethrough, the valve member 8 ismoved upwardly as viewed in FIG. 4 due to a pressure difference betweenthe second resin path 4 and the third resin path 5 to close the secondresin path 4 as shown in FIG. 5.

Thereby, only the same molten resin A is injected into the cavity 16.The different molten resin B of the second resin path 4 is not injected.

Subsequently, at the time of completion of the injection of apredetermined quantity of molten resin A into cavity 16, and wheninjection pressure is applied to the second resin path 4, the valvemember 8 is moved downward, as shown in FIG. 4, due to a difference in apressure receiving are in the valve member 8, to open the second resinpath 4 so that the molten resin B is injected between the two paths ofmolten resin A coming from the first and third resin paths 3 and 5. Thethree resin layers are then injected into the cavity 16 from theinjection opening 2.

After the aforesaid injection has been completed, a product having threelayers as a whole is molded, and when injection pressure of the secondresin path 4 is disconnected, the valve member 8 is again moved forwardby the resin pressure of the third resin path 5, as shown in FIG. 5, dueto a difference in resin pressure at that time, to close the secondresin path 4.

Therefore, only the molten resin A is again injected into cavity 16, anda single layer is molded. The molten resin B injected from the secondresin path 4 is to be positioned in the center between the two layers ofmolten resin A, and therefore, when the resin is filled and moved in thecavity 16, even if a skin layer caused by cooling should occur on thesurfaces of the two layers of molten resin A in contact with the moldsurface, the skin layer has a slow influence thereon and it is difficultfor the molten resin B to form a skin layer halfway.

The molded product 20 shown in FIG. 6 is a preform having a bottomcomprising a mouth portion 21 formed of three layers by injecting andfilling the molten resin B of the second resin path 4 and a body 22 anda bottom 23 both formed of a single layer only formed of molten resin A,the chain line indicating a container 30 in which a preform having abottom is orientation blow molded.

The molded product 40 shown in FIG. 7 is a preform having a three-layerbody 42 (obtained by injecting the molten resin B of the second resinpath 4 in between the molten resin A of the first and third resin paths3, 5) and a mouth portion 4a and a bottom portion 43 both formed of asingle layer of resin A. The chain line indicates a container 50 inwhich a preform having a bottom is orientation blow molded.

The molded product 60 shown in FIG. 8 is a preform having a three-layerbottom 73 (obtained by injecting the molten resin B of the second resinpath 4 in between the molten resin A of the first and third resin paths3, 5) and a mouth portion 61 and a body portion 62 formed of a singlelayer of resin A. The chain line indicates a container 70 in which apreform having a bottom is orientation blow molded.

The resin used as the molten resin A may comprise a resin such as apolyethylene terephthalate, and the molten resin B includes resinsexcellent in barrier properties such as methaxylene group containedpolyamide, ethylene vinyl alcohol and high nitrile or resins having aheat resistance such as polycarbonate and U-polymer® (a trademark ofUnichika Co., Ltd registered in Japan), which are used according to usesof containers molded thereby.

For example, when a resin forming an intermediate layer 34 comprises apolycarbonate, formation of a mouth portion 31 of a container 30 into amulti-layer remarkably improves the heat resistance as compared with thecase where it merely comprises a polyethylene terephthalate to preventthe mouth portion from being changed during heating and filling.

Similarly, when a bottom 73 of a container 70 (FIG. 8) is formed into amulti-layer by an intermediate layer 74 of U-shaped polymer, the heatresistance of the bottom 73 is improved, and even if heat treatment isconducted after filling a carbonated juice, a central portion thereof isnot projected and deformed as in a bottom of a single layer.

Furthermore, in a product in which only a body 52 is formed into amulti-layer by an intermediate layer formed of a methaxylene groupcontained polyamide, barrier properties are improved, peeling betweenlayers when a bottom is formed into a multilayer can be prevented, andexpensive resins used for the intermediate layer 54 can be saved.

Next, one example of molding conditions in the case of the three-layernozzle shown in FIG. 1 is given below.

Sectional area of resin paths

First resin path: 34.56 mm²

Second resin path: 59.69 mm²

Third resin path: 21.23 mm²

Diameter of injection opening 2.0 to 3.0 mm

Pressure receiving area (projection area) of valve member

Second resin path side (fore end): 25.13 mm²

Third resin path side (rear end): 21.23 mm²

Resin material

First and third resin paths

Polyethylene terephthalate

Second resin path

SM nylon

Injection pressure

First and third resin paths

Primary pressure: 140 kg/cm²

Secondary pressure: 58 kg/cm²

Second resin path: 100 kg/cm²

As mentioned above, according to this invention, a first, a second and athird resin paths are concentrically provided within a nozzle body, thesecond resin path being closed by a valve member which is actuated byresin pressure of the other resin paths to control a molten resin fromthe second resin path, whereby a position at which an intermediate layeris formed by the molten resin can be suitably set. Therefore, only themouth portion, body or bottom of a molded product can be formed into amultilayer. Since the position of the intermediate layer can be set to acentral portion, in injection molding of a multi-layer molded product,the effect is great, and it is industrially very effective and widelyutilized.

We claim:
 1. A multilayer nozzle, comprising:a first core memberdefining a generally cylindrical first resin path; a second core memberencircling said first core member and cooperating with said first coremember to define a generally cylindrical second resin path; a nozzlebody encircling said second core member and cooperating with said secondcore member to define a generally cylindrical third resin path; saidfirst, second and third resin paths being concentric with one anotherand directing resin passing through them to a common injection opening;a valve member cooperating with said second resin path and separate fromsaid core members and said nozzle body and movable between a firstposition wherein it closes said second resin path and a second positionwherein it opens said second resin path; responsive means associatedwith the valve member responsive to respective pressures of first andsecond resins injected into said first and second paths, respectively,to move said valve member between said first and second positions inresponse to changes in said respective pressures of said first andsecond resins in said first and second paths; and said first and secondcore members, said nozzle body and said valve member cooperating tocreate a multilayer resin from said first and second resins and a thirdresin injected under pressure into said third resin path, saidmultilayer resin having said second resin sandwiched between said firstand third resins when said valve member is in said second position andwhen said first, second and third resins are injected through saidfirst, second and third resin paths, respectively.
 2. The multilayernozzle of claim 1, wherein said valve member has respective faces facingsaid first and second resin paths, said faces defining said responsivemeans and causing said valve member to move between said first andsecond positions in response to said respective pressures applied tosaid respective faces by said first and second resins in said first andsecond paths.
 3. The multilayer nozzle of claim 2, wherein said valvemember is supported by said first core member for movement between saidfirst and second positions.
 4. The multilayer nozzle assembly of claim3, wherein said first core member terminates at a distal end and saidvalve member is located on said distal end of said first core member. 5.The multilayer nozzle of claim 2, wherein said respective faces arefirst and second tapered surfaces each forming a respective obliqueangle with a central axis of said nozzle and facing said first andsecond resin paths to define first and second pressure receiving areas.6. The multilayer nozzle of claim 5, wherein the ratio between saidfirst and second pressure receiving areas of said first and secondsurfaces is greater than 0.5 and less than
 4. 7. The multilayer nozzleof claim 2, further comprising means for injecting said first, secondand third resins under pressure into said first, second and third resinspath, respectively.
 8. The multilayer nozzle of claim 1, wherein saidvalve member is movable relative to said first core member, said secondcore member and said nozzle body.
 9. The multilayer nozzle of claim 8,further including means for simultaneously injecting said first, secondand third resins into said first, second and third resin paths,respectively, so as to cause said first and second core members, saidnozzle body and said valve member to cooperate to create saidmulti-layer resin.
 10. The multilayer nozzle of claim 1, furtherincluding means for simultaneously injecting said first, second andthird resins into said first, second and third resin paths,respectively, so as to cause said first and second core members, saidnozzle body and said valve member to cooperate to create saidmulti-layer resin.
 11. The multilayer nozzle of claim 1, wherein saidfirst and second core members and said nozzle body are stationaryrelative to one another.
 12. A multilayer nozzle, comprising:a firstcore member defining a generally cylindrical first resin path; a secondcore member encircling said first core member and cooperating with saidfirst core member to define a generally cylindrical second resin path; anozzle body encircling said second core member and cooperating with saidsecond core member to define a generally cylindrical third resin path;said first, second and third resin paths being concentric with oneanother and directing resin passing through them to a common injectionopening; a valve member cooperating with said second resin path andmovable between a first position wherein it closes said second resinpath and a second position wherein it opens said second resin path;responsive means associated with the valve member responsive torespective pressures of first and second resins injected into saidsecond and third resin paths, respectively, to move said valve memberbetween said first and second positions in response to changes in saidrespective pressures of said first and second resins in said second andthird paths; and said first and second core members, said nozzle bodyand said valve member cooperating to create a multilayer resin from saidfirst and second resins and a third resin injected under pressure intosaid first resin path, said multilayer resin having said first resinsandwiched between said second and third resins when said valve memberis in said second position and when said first, second and third resinsare injected through said second, said third and said first resin paths,respectively.
 13. The multilayer nozzle of claim 12, wherein said valvemember has respective faces facing said second and third resin paths,said faces defining said responsive means and causing said valve memberto move between said first and second positions in response to therelative pressures applied to said respective faces by said first andsecond resins in said second and third paths.
 14. The multilayer nozzleof claim 13, wherein said valve member is supported by said second coremember for movement between said first and second positions.
 15. Themultilayer nozzle of claim 14, wherein said second core memberterminates at a distal end and said valve member is located on saiddistal end of said second core member.
 16. The multilayer nozzle ofclaim 13, wherein said respective faces are first and second taperedsurfaces each forming an oblique angle with a central axis of said resinpaths and abutting said second and third resin paths to define first andsecond pressure receiving areas.
 17. The multilayer nozzle of claim 16,wherein the ratio between said first and second pressure receiving areasof said first and second surfaces is greater than 0.5 and less than 4.18. The multilayer nozzle of claim 17, further including means forinjecting said first, second and third resins into said second, thirdand first resin paths, respectively.
 19. A multilayer nozzle,comprising:a first core member defining a generally cylindrical firstresin path; a second core member encircling said first core member andcooperating with said first core member to define a generallycylindrical second resin path; a nozzle body encircling said second coremember and cooperating with said second core member to define agenerally cylindrical third resin path; said first, second and thirdresin paths being concentric with one another and directing resinpassing through them to a common injection opening; a valve membercooperating with said second resin path and movable relative to saidfirst core member, said second core member and said nozzle body betweena first position wherein it closes said second resin path and a secondposition wherein it opens said second resin path; means associated withthe valve member responsive to respective pressures of first and secondresins injected into said first and second paths, respectively, to movesaid valve member between said first and second positions in response tochanges in said respective pressures of said first and second resins insaid first and second paths; and said first and second core members,said nozzle body and said valve member cooperating to create amultilayer resin from said first and second resins and a third resininjected under pressure into said third resin path, said multilayerresin having said second resin sandwiched between said first and thirdresins when said valve member is in said second position and when saidfirst, second and third resins are injected through said first, secondand third resin paths, respectively.
 20. A multilayer nozzle,comprising:a first core member defining a generally cylindrical firstresin path; a second core member encircling said first core member andcooperating with said first core member to define a generallycylindrical second resin path; a nozzle body encircling said second coremember and cooperating with said second core member to define agenerally cylindrical third resin path; said first, second and thirdresin paths being concentric with one another and directing resinpassing through them to a common injection opening, said first coremember, said second core member and said nozzle body being stationaryrelative to one another; a valve member cooperating with said secondresin path and movable between a first position wherein it closes saidsecond resin path and a second position wherein it opens said secondresin path; means associated with said valve member responsive torespective pressures of first and second resins injected into said firstand second paths, respectively, to move said valve member between saidfirst and second positions in response to changes in said respectivepressures of said first and second resins in said first and secondpaths; and said first and second core members, said nozzle body and saidvalve member cooperating to create a multilayer resin from said firstand second resins and a third resin injected under pressure into saidthird resin path, said multilayer resin having said second resinsandwiched between said first and third resins when said valve member isin said second position and when said first, second and third resins areinjected through said first, second and third resin paths, respectively.21. A multilayer nozzle, comprising:a first core member defining agenerally cylindrical first resin path; a second core member encirclingsaid first core member and cooperating with said first core member todefine a generally cylindrical second resin path; a nozzle bodyencircling said second core member and cooperating with said second coremember to define a generally cylindrical third resin path; said first,second and third resin paths being concentric with one another anddirecting resin passing through them to a common injection opening; avalve member cooperating with said second resin path and movable betweena first position wherein it closes said second resin path and a secondposition wherein it opens said second resin path; means associated withthe valve member responsive to respective pressures of first and secondresins injected into said first and second paths, respectively, to movesaid valve member between said first and second positions in response tochanges in said respective pressures of said first and second resins insaid first and second paths; means for simultaneously injecting saidfirst resin, said second resin and a third resin into said first, secondand third resin paths, respectively, the respective pressures of saidfirst and second resins causing said valve member to move into saidsecond position; and said first and second core members, said nozzlebody and said valve member cooperating to create a multilayer resin fromsaid first, second and third resins, said second resin being sandwichedbetween said first and third resins.